<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8" />
    <title>异步绘图</title>
    <style>
        body {
            margin: 0;
            overflow: hidden;
        }
        #canvas {
            background-color: antiquewhite;
        }
    </style>
</head>
<body>
<canvas id="canvas"></canvas>
<!-- 顶点着色器 -->
<script id="vertexShader" type="x-shader/x-vertex">
      attribute vec4 a_Position;
      void main(){
          gl_Position=a_Position;
          gl_PointSize=20.0;
      }
    </script>
<!-- 片元着色器 -->
<script id="fragmentShader" type="x-shader/x-fragment">
      void main(){
          gl_FragColor=vec4(1,1,0,1);
      }
    </script>
<script type="module">
  import { initShaders } from "../jsm/Utils.js";

  const canvas = document.querySelector("#canvas");
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;

  // 获取着色器文本
  const vsSource = document.querySelector("#vertexShader").innerText;
  const fsSource = document.querySelector("#fragmentShader").innerText;

  //三维画笔
  const gl = canvas.getContext("webgl");

  //初始化着色器
  initShaders(gl, vsSource, fsSource);

  //顶点数据
  let vertices=[0, 0.2]
  //缓冲对象
  const vertexBuffer = gl.createBuffer();
  //绑定缓冲对象
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
  //写入数据
  gl.bufferData(gl.ARRAY_BUFFER,new Float32Array(vertices),gl.STATIC_DRAW)
  //获取attribute 变量
  const a_Position=gl.getAttribLocation(gl.program, 'a_Position')
  //修改attribute 变量
  gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0)
  //赋能-批处理
  gl.enableVertexAttribArray(a_Position)

  //声明颜色 rgba
  gl.clearColor(0, 0, 0, 1);
  //刷底色
  gl.clear(gl.COLOR_BUFFER_BIT);
  //绘制顶点
  gl.drawArrays(gl.POINTS, 0, 1);


  setTimeout(()=>{
    vertices.push(-0.2,-0.1)
    gl.bufferData(gl.ARRAY_BUFFER,new Float32Array(vertices),gl.STATIC_DRAW)
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.drawArrays(gl.POINTS, 0, 2);
  },1000)

  setTimeout(()=>{
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.drawArrays(gl.POINTS, 0, 2);
    gl.drawArrays(gl.LINE_STRIP, 0, 2);
  },2000)

</script>
</body>
</html>
